There has been a continuing need for improved bone graft materials. Although autograft, the current gold standard, may have very good properties and radiopacity, its use exposes patients to the risk of second surgeries, pain, and morbidity at the donor site. Allograft devices, which are processed from donor bone, also have very good radiopacity, but carry the risk of disease transmission. The devices are restricted in terms of variations on shape and size and have sub-optimal strength properties that decrease after implantation. The quality of the allograft devices varies because they are natural. Also, since companies that provide allograft implants obtain their supply from donor tissue banks, there tend to be limitations on supply. In recent years, synthetic materials have become a viable alternative to autograft and allograft devices. One such synthetic material is Vitoss® Scaffold Synthetic Cancellous Bone Void Filler (Orthovita, Inc., Malvern, Pa., assignee of the present application). Synthetic graft materials, like autograft and allograft, serve as osteoconductive scaffolds that promote the ingrowth of bone. As bone growth is promoted and increases, the graft material resorbs and is eventually replaced with new bone.
Many synthetic bone grafts include materials that closely mimic mammalian bone, such as compositions containing calcium phosphates. Exemplary calcium phosphate compositions contain type-B carbonated hydroxyapatite [Ca5(PO4)3x(CO3)x(OH)], which is the principal mineral phase found in the mammalian body. The ultimate composition, crystal size, morphology, and structure of the body portions formed from the hydroxyapatite are determined by variations in the protein and organic content. Calcium phosphate ceramics have been fabricated and implanted in mammals in various forms including, but not limited to, shaped bodies and cements. Different stoichiometric compositions such as hydroxyapatite (HAp), tricalcium phosphate (TCP), tetracalcium phosphate (TTCP), and other calcium phosphate salts and minerals, have all been employed to match the adaptability, biocompatibility, structure, and strength of natural bone. The role of pore size and porosity in promoting revascularization, healing, and remodeling of bone has been recognized as a critical property for bone grafting materials. The preparation of exemplary porous calcium phosphate materials that closely resemble bone have been disclosed, for instance, in U.S. Pat. Nos. 6,383,519 and 6,521,246, incorporated herein by reference in their entirety.
There has been a continued need for improved bone graft systems. Although calcium phosphate bone graft materials are widely accepted, they lack the strength, handling and flexibility necessary to be used in a wide array of clinical applications. Heretofore, calcium phosphate bone graft substitutes have been used in predominantly non-load bearing applications as simple bone void fillers and the like. For more clinically challenging applications that require the graft material to take on load, bone reconstruction systems that pair a bone graft material to traditional rigid fixation systems are used. The prior art discloses such bone reconstruction systems. For instance, MacroPore OS™ Reconstruction System is intended to reinforce and maintain the relative position of weak bony tissue such as bone graft substitutes or bone fragments from comminuted fractures. The system is a resorbable graft containment system composed of various sized porous sheets and sleeves, non-porous sheets and sleeves, and associated fixation screws and tacks made from polylactic acid (PLA). However, the sheets are limited in that they can only be shaped for the body when heated. Further, these materials lack an absorbent component and, therefore, are not suitable for the delivery and sustained release of materials of the types described herein.
The Synthes SynMesh™ consists of flat, round, and oval shaped cylinders customized to fit the geometry of a patient's anatomical defect. The intended use is for reinforcement of weak bony tissue and is made of commercially pure titanium. Although this mesh may be load bearing, it lacks an absorbant component for the delivery of materials of the types described herein.
Many bone graft materials have limited interconnectedness that substantially limits their ability to retain and deliver therapeutic materials and fluids at a bony site. As such, these graft materials would not be suitable as carriers for therapeutic materials and fluids such as cells, cell signaling materials, proteins, bone marrow aspirate, and blood. It is also known that most bone graft materials lack the structural integrity necessary to provide support.
Conversely, metals, which are capable of providing structural support typically are not readily absorbent and cannot retain fluid. This is also due in part to their low porosity or macro-hole structures.
It would be of great benefit in the art to use graft materials for the retention and delivery of therapeutic materials or fluids. Currently, bone grafts often are incapable of adequately retaining fluids once a surgeon attempts to implant the graft into a bony space. The majority of the fluids are flushed out of the graft when manipulated by the surgeon. Thus, there is a need in the art for a bone graft capable of retaining and delivering therapeutic materials that are at least partially load bearing.
There is a need for resorbable bone grafts with improved handling, which are flexible and not brittle, and are compression resistant. It has been discovered that admixing highly porous resorbable inorganic bodies with resorbable polymeric materials greatly improves upon handling, yet still provides an osteoconductive implant with good resorption and bone formation properties. It will be appreciated that such an implant would offer an easy-to-use dose of composite material and would be an advancement over current bone reconstruction systems for certain clinical applications in that it eliminates the need to have both a graft material and rigid fixation system.
There is a need in the art to provide biocompatible graft materials with exceptional osteoconductive properties; to provide pre-sized graft materials in a variety of forms, including strips and cylinders for restoring defects in bone; to provide bone graft materials that can be shaped; and to provide bone graft materials with improved handling properties, so that the graft material can be cut while dry or after being wetted and does not crumble.
Also called for are bone graft materials with some compression resistance, such that the brittleness often associated with inorganic or ceramic bone graft materials is eliminated. There is also a need for bone graft materials with integrity that are at least partially load bearing; graft materials with improved pliability that still retain high degrees of porosity over a broad pore size distribution to maintain superior resorption and bone ingrowth properties; and bone graft materials with fluid wicking and retention properties even under compressive loads.
The art would benefit from bone grafts that provide easy implantation into a bony space and with decreased tendency to wash away when imbibed with fluid and bone graft materials that are highly suitable for retaining and wicking therapeutic fluid materials.
Objects, advantages, and novel features of this invention will become apparent to those skilled in the art upon examination of the following descriptions, figures and claims thereof, which are not intended to be limiting.